This invention relates to an improved vertical signature stacker. This type of stacker is already widely known, as evidenced, for example, by U.S. Pat. No. 3,969,993. Essentially, these vertical stackers comprise a stacker framework, conveyor belts for supporting the signatures delivered by a rotary press, an outer separator plate designed to interrupt the continuous flow of incoming signatures and form the initial part of the stack, translation guides and powered units designed to raise and lower the separator plate, a fork onto which the stacks delivered by the separator plate are placed, said fork being supplied with translation guides and with powered units governing the upward and downward motion of same, a sliding wall for lowering the stacks and a bottom wall for supporting the stacks so formed, said sliding and bottom walls being provided in the form of roller boards.
The separator plate, with the relevant jack controlling the forward and reverse motion of same, is hinged onto an outer support located in the upper front section of the stackers and, more specifically, in such a way that when the plate reaches its bottom limit stop position, it is roughly equal in height to the stacker operator. This design entails a number of shortcomings and disadvantages, the most serious of which shall be referred to hereinafter. At the end of its downstroke, the separator plate reaches a height where it is roughly level with the head of the operator; after reaching this position, the plate is tilted upwards, and the upstroke is effected. Besides causing considerable inconvenience, these movements may prove a serious hazard to the operator's safety. In addition, as the separator plate runs along a plane which cuts across the middle of the stacker, the operator tends to stand either to the right or to the left of the stacker, which makes it somewhat more difficult to follow closely all the steps involved in the stacking process. Since the strokes of the separator plates normally measure approximately 40 cms and the height of the plate in its lowermost position ranges from 180 to 190 cms, it readily follows that the overall height of the stackers adds up to roughly 220-230 cms. This design, therefore, implies significant additional construction costs and, furthermore, fails to take into account some basic operative requirements, in that the operator must virtually "climb" up the stacker in order to gain access to the upper section thereof and to adjust and line up the upper stacking positioners. Moreover, the higher the construction, the greater the length of the signature conveyor belts required for its operation; this, in turn, means that more powerful equipment must be used in order to drive said belts and that expensive, tailor-made guide pulleys must be employed. A further disadvantage inherent in these exceedingly high stackers is that the relevant conveyor belt paths feature a steeply sloping section, which often results in undesired slippage or overlapping of signatures, e.g. where coated paper is used.
Conventional vertical stackers present other shortcomings, in that both the separator plate and the fork are operated by a single electric motor featuring a dual friction clutch as regards the downstrokes of the plate and fork, whereas the upstrokes of same are effected by means of pneumatic cylinder-ram units. The fork-driving pneumatic cylinder-ram unit also acts as a braking device when the stack is lowered at considerable speed after its completion. In addition to the fact that these pneumatic units entail substantial costs, it is worth noting that said pneumatic braking devices are rather difficult to calibrate, for the stacks, while lowered from one and the same height, may vary in weight depending on the degree of compactness of the relevant signatures. These pneumatic units are furthermore ineffective in interrupting or reducing the speed of the downstroke of the fork, while this would be desirable in the extreme in order to ensure proper automatic loading of the endboards which are normally placed at the upper ends of the stacks.
While conventional vertical stackers feature a steeply sloping conveyance section, they may sometimes require a relatively long conveyance path in order to avoid the exceedingly steep slopes which may result from direct connection to the rotary press, as these would pose additional difficulties in terms of an even conveyance of the scaled stream of signatures. This necessarily implies a considerable overall width, while printing shops are normally rather small in size and therefore require a most efficient use of the space available. The adoption of bulky equipment, such as the stackers described hereinabove, may sometimes require additional work in order to accommodate the equipment itself in the existing facilities.